Thread: Zenith idling issues.

I have a series 3, 4 cyl with a zenith carb. When idling the idle speed varies constantly of its own accord. Does anyone have any suggestions on how to stop this? Thanks

Not necessarily the carburetter! Check also for worn distributor, vacuum leaks, poor valve seating.

But certainly the carburetter can cause this. There are two likely problems.

1. Worn throttle spindle/bushes. There should be no appreciable play on the throttle shaft, if there is it probably needs a new shaft and the body rebushing.

2. Warped top cover allowing the the top gasket and/or O-ring to leak. Remove the top cover, and disassemble it completely test the mating surface for flatness on a sheet of plate glass. If not flat, put a sheet of fine (600+) wet and dry on the glass, and carefully lap it flat. Check the top of the main body is flat as well. When reassembling, check that the heads of the screws holding the emulsion block are not hitting the main body (If they are, either the screws or washers are not original or there is a burr on them.

Hope this helps,

John